The said drawbacks are eliminated by the immobilisation of the silver nanoparticles on solid substrates, principle of which is that the immobilisation occurs in two steps, where in the first step the selected substrate is modified by polyethylenimine (PEI) with branched structure by simple submerging of the selected substrate to a bath consisting of aqueous solution of this polymer and then, the excess is washed off the Substrate surface after removal from the bath and in the second step the PEI modified substrate is submerged to the silver salt solution where the production of the nanoparticles proceeds, these to the reduction properties of —NH and —NH2 of polymer functional groups, and the nanoparticles remain covalently immobilised to the primary deposited adhesive PEI layer of polyethylenimine.
The main benefit of the two-step immobilisation of the silver nanoparticles on solid substrates using polyethylenimine as the adhesive and reduction linker is that the primary coating of solid substrates by polyethylenimine occurs followed by production of silver nanoparticles covalently anchored on polymer surface thanks to the reduction effect of its functional groups and therefore, no nanoparticles are released to the environment. The two-step covalently immobilised nanoparticles, contrary to single step method where the particle surface is covered by polymer, maintain large free surface area that can be used for interaction with microorganisms.
Favourably, distilled water is used for washing of the solid substrates containing the immobilised silver nanoparticles.
Also favourable is that the reduction of the silver ions occurs without an external reducing agent using only a slight temperature activation. Current reduction and immobilization take place at temperature 60° C. and for 20 minutes. The synthesis of the composite is finished by repeated washing of the substrate—PEI—nanosilver composite with water, which removes potential excessive ion silver coming from the precursor.
The described procedure for immobilisation of the silver nanoparticles has the following benefits:                a) covalent immobilisation of the nanoparticles demonstrably occurs and the risk of their release to environment is mitigated;        b) the proposed method of immobilisation does not use an external reducing agent because the functional groups in PEI play the role;        c) the proposed method of immobilisation does not use a stabiliser because no surface aggregation of particles occurs due to covalent immobilisation;        d) the proposed method is very cheap, not demanding and quick with respect to experiments, occurs under aqueous conditions and no toxic substances are used;        e) the method is derrionstrably universal and applicable to modification of different surface types including plastics, textile fibres and filter fibres.        
In addition to the elimination of all disadvantages of other published and proposed immobilisation procedures, the proposed procedure has obviotaly the following application advantages:                f) non-toxicity and bio-compatibility of PEI;        g) excellent adhesion properties of PEI to any solid substrate;        h) favourable use of PEI with branched structure and high molecular height, which—with respect to high number of functional groups in the chain—enables production of small nanoparticles of uniform size distribution and homogeneous distribution on substrate surface; average size of the silver particles produced in this way is about 40 nm (regardless nature of solid substrate) and the particles of this size provides high anti-bacterial effect;        i) employment of two-step immobilisation method is favourable as well. In case of procedures commonly appearing in bibliography, where polymer is used for the reduction of silver ions without primary coating on a solid substrate, significant coating of surface of the reduced silver nanoparticles by polymer followed by the inactivation of surface from the anti-microbial point of view. However, similar effect may also occur in case of one-step immobilisation on solid substrate, unless, excessive polymer is removed. Obviously, the two-step immobilisation clearly allows production of the nanoparticles with predominantly free surface and seamless removal of excessive polymer and silver.        